U.S. patent application number 14/688916 was filed with the patent office on 2015-08-06 for systems and methods for digital video stabilization via constraint-based rotation smoothing.
The applicant listed for this patent is Facebook, Inc.. Invention is credited to Alexandre Karpenko.
Application Number | 20150222818 14/688916 |
Document ID | / |
Family ID | 49726634 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150222818 |
Kind Code |
A1 |
Karpenko; Alexandre |
August 6, 2015 |
SYSTEMS AND METHODS FOR DIGITAL VIDEO STABILIZATION VIA
CONSTRAINT-BASED ROTATION SMOOTHING
Abstract
Systems and methods for digital video stabilization via
constraint-based rotation smoothing are provided. Digital video
data including a set of image frames having associated time stamps
and a set of camera orientation data having associated time stamps
may be provided. A smoothed set of camera orientation data may be
generated by minimizing a rate of rotation between successive image
frames while minimizing an amount of empty regions in a resulting
set of smoothed image frames reoriented based on the smoothed set
of camera orientation data.
Inventors: |
Karpenko; Alexandre; (Palo
Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook, Inc. |
Menlo Park |
CA |
US |
|
|
Family ID: |
49726634 |
Appl. No.: |
14/688916 |
Filed: |
April 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14101252 |
Dec 9, 2013 |
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14688916 |
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61735976 |
Dec 11, 2012 |
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Current U.S.
Class: |
348/208.6 |
Current CPC
Class: |
G11B 27/11 20130101;
H04N 5/23267 20130101; H04N 5/23258 20130101; H04N 5/77 20130101;
H04N 5/91 20130101; H04N 5/2329 20130101 |
International
Class: |
H04N 5/232 20060101
H04N005/232 |
Claims
1. A computer-implemented method comprising: acquiring, by a
computing system, video data comprising a set of image frames
having associated time stamps; acquiring, by the computing system,
a set of camera orientation data having associated time stamps,
wherein the set of camera orientation data is based on an
orientation of a camera while the video data is being acquired by
the camera; and reorienting, by the computing system, each
particular image frame in at least a subset of the set of image
frames based on an associated subset of the camera orientation
data.
2. The computer-implemented method of claim 1, wherein each
particular image frame has a respective time stamp, and wherein the
associated subset of the camera orientation data for each
particular image frame also has the respective time stamp.
3. The computer-implemented method of claim 2, wherein each
particular image frame is reoriented based on rotating each
particular image frame to counteract undesired shaking indicated
via the associated subset of the camera orientation data for each
particular image frame.
4. The computer implemented method of claim 3, wherein the
undesired shaking indicated via the associated subset of the camera
orientation data introduces deformation to each particular image
frame, and wherein each particular image frame is rotated to
counteract the deformation.
5. The computer-implemented method of claim 1, wherein reorienting
each particular image frame in at least the subset of the set of
image frames produces a resulting set of smoothed image frames, and
wherein reorienting each particular image frame in at least the
subset of the set of image frames further comprises: minimizing a
rate of rotation between each particular image frame and another
image frame in at least the subset of the set of image frames while
minimizing an amount of empty regions in the resulting set of
smoothed image frames.
6. The computer-implemented method of claim 5, wherein minimizing
the amount of empty regions in the resulting set of smoothed image
frames further comprises: performing at least one of a cropping
operation or a zooming operation with respect to each particular
image frame in at least the subset of the set of image frames.
7. The computer-implemented method of claim 5, wherein each
particular image frame and the other image frame correspond to
successive image frames.
8. The computer-implemented method of claim 1, wherein the set of
camera orientation data provides a representation of the
orientation of the camera.
9. The computer-implemented method of claim 1, wherein the set of
camera orientation data is acquired by one or more orientation
sensors, wherein the one or more orientation sensors are included
in the computing system, and wherein the computing system
corresponds to at least one of a computing device including the
camera or a server remote from the camera.
10. The computer-implemented method of claim 9, wherein the one or
more orientation sensors include at least one of a gyroscope or an
accelerometer.
11. A system comprising: at least one processor; and a memory
storing instructions that, when executed by the at least one
processor, cause the system to perform: acquiring video data
comprising a set of image frames having associated time stamps;
acquiring a set of camera orientation data having associated time
stamps, wherein the set of camera orientation data is based on an
orientation of a camera while the video data is being acquired by
the camera; and reorienting each particular image frame in at least
a subset of the set of image frames based on an associated subset
of the camera orientation data.
12. The system of claim 11, wherein each particular image frame has
a respective time stamp, and wherein the associated subset of the
camera orientation data for each particular image frame also has
the respective time stamp.
13. The system of claim 12, wherein each particular image frame is
reoriented based on rotating each particular image frame to
counteract undesired shaking indicated via the associated subset of
the camera orientation data for each particular image frame.
14. The system of claim 13, wherein the undesired shaking indicated
via the associated subset of the camera orientation data introduces
deformation to each particular image frame, and wherein each
particular image frame is rotated to counteract the
deformation.
15. The system of claim 11, wherein reorienting each particular
image frame in at least the subset of the set of image frames
produces a resulting set of smoothed image frames, and wherein
reorienting each particular image frame in at least the subset of
the set of image frames further comprises: minimizing a rate of
rotation between each particular image frame and another image
frame in at least the subset of the set of image frames while
minimizing an amount of empty regions in the resulting set of
smoothed image frames.
16. A non-transitory computer-readable storage medium including
instructions that, when executed by at least one processor of a
computing system, cause the computing system to perform a method
comprising: acquiring video data comprising a set of image frames
having associated time stamps; acquiring a set of camera
orientation data having associated time stamps, wherein the set of
camera orientation data is based on an orientation of a camera
while the video data is being acquired by the camera; and
reorienting each particular image frame in at least a subset of the
set of image frames based on an associated subset of the camera
orientation data.
17. The non-transitory computer-readable storage medium of claim
16, wherein each particular image frame has a respective time
stamp, and wherein the associated subset of the camera orientation
data for each particular image frame also has the respective time
stamp.
18. The non-transitory computer-readable storage medium of claim
17, wherein each particular image frame is reoriented based on
rotating each particular image frame to counteract undesired
shaking indicated via the associated subset of the camera
orientation data for each particular image frame.
19. The non-transitory computer-readable storage medium of claim
18, wherein the undesired shaking indicated via the associated
subset of the camera orientation data introduces deformation to
each particular image frame, and wherein each particular image
frame is rotated to counteract the deformation.
20. The non-transitory computer-readable storage medium of claim
16, wherein reorienting each particular image frame in at least the
subset of the set of image frames produces a resulting set of
smoothed image frames, and wherein reorienting each particular
image frame in at least the subset of the set of image frames
further comprises: minimizing a rate of rotation between each
particular image frame and another image frame in at least the
subset of the set of image frames while minimizing an amount of
empty regions in the resulting set of smoothed image frames.
Description
PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/101,252, filed on Dec. 9, 2013 entitled
"SYSTEMS AND METHODS FOR DIGITAL VIDEO STABILIZATION VIA
CONSTRAINT-BASED ROTATION SMOOTHING" which claims the benefit of
priority to U.S. Provisional Patent Application No. 61/735,976,
filed Dec. 11, 2012, the entireties of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The subject matter of the present disclosure relates to
signal processing. More particularly, the present disclosure
relates to systems and methods for image and video processing.
BACKGROUND
[0003] Digital still cameras capable of capturing video have become
widespread in recent years. While the resolution and image quality
of these consumer devices has improved up to the point where they
rival digital single-lens reflex cameras (DSLRs) in some settings,
their video quality may still be significantly worse than that of
film cameras. The reason for this gap in quality may be twofold.
First, compared to film cameras, cell phones may be significantly
lighter. As a result, hand-held video capture on such devices may
exhibit a greater amount of camera shake. Second, cell-phone
cameras may have sensors that make use of a rolling shutter (RS).
In an RS camera, each image row may be exposed at a slightly
different time, which, combined with undampened camera motion, may
result in a "wobble" in the output video.
[0004] Video stabilization is a family of techniques used to reduce
high-frequency frame-to-frame jitter produced by video camera
shake. In professional cameras, mechanical image stabilization
(MIS) systems are commonly used. For example, in an MIS system, the
operator may wear a harness that separates the camera's motion from
the operator's body motion. Other MIS systems stabilize the optics
of the camera rather than the camera body itself. These systems may
move the lens or sensor to compensate for small pitch and yaw
motions. These techniques work in real time and do not require
computation on the camera. However, they are not suitable for
mobile devices and inexpensive cameras, because of their price and
size. Digital video stabilization systems may employ feature
trackers to stabilize videos post-capture. However, these systems
may be sensitive to noise (e.g., fast moving foreground objects)
and require distinctive features for tracking. As a result, digital
stabilization based on feature tracking often breaks down,
especially in adverse lighting conditions and excessive foreground
motion. In addition, extracting and matching visual cues across
frames can be computationally expensive. Furthermore, the expense
grows with the resolution of the video. In some instances, this may
be too costly to perform video stabilization in real time.
Consequently, such approaches are rarely employed in current
digital cameras. Instead, manufacturers can opt for more robust
(and expensive) mechanical stabilization solutions for high-end
DSLRs.
SUMMARY OF THE INVENTION
[0005] To stabilize digital video, computer implemented methods,
systems, and computer readable media, in an embodiment, may provide
digital video data including a set of image frames having
associated time stamps and a set of camera orientation data having
associated time stamps. A smoothed set of camera orientation data
may be generated by minimizing a rate of rotation between
successive image frames while minimizing an amount of empty regions
in a resulting set of smoothed image frames reoriented based on the
smoothed set of camera orientation data.
[0006] In an embodiment, the amount of empty regions in the
resulting set of smoothed image frames may be minimized to
zero.
[0007] In an embodiment, the amount of empty regions in the
resulting set of smoothed image frames may be minimized below a
threshold value.
[0008] In an embodiment, the set of image frames may be warped
based on the associated time stamps for the set of image frames and
the smoothed set of camera orientation data to form a set of
corrected image frames.
[0009] In an embodiment, the warping of the set of image frames
based on the associated time stamps for the set of image frames and
the smoothed set of camera orientation data to form a set of
corrected image frames may include dividing an individual image
frame into a plurality of subsections. Each subsection may have an
associated time stamp and camera orientation. The warping of the
set of image frames based on the associated time stamps for the set
of image frames and the smoothed set of camera orientation data to
form a set of corrected image frames may include realigning each
subsection based on the associated time stamp and camera
orientation to form an individual corrected image frame.
[0010] In an embodiment, the set of corrected image frames may be
displayed as a video.
[0011] In an embodiment, the amount of empty regions in the
resulting set of smoothed image frames may be minimized below a
threshold value.
[0012] In an embodiment, the amount of empty regions below the
threshold value may be inpainted.
[0013] In an embodiment, the set of camera orientation data having
associated time stamps may be provided from a gyroscope of a
handheld device.
[0014] In an embodiment, the set of image frames may be provided
from a camera of a handheld device.
[0015] In an embodiment, the set of camera orientation data having
associated time stamps may be provided from a gyroscope of a
handheld device including a mobile phone and a digital camera. The
set of image frames may be provided from the digital camera.
[0016] In an embodiment, the generating of the smoothed set of
camera orientation data includes an iterative optimization based on
gradient descent.
[0017] In an embodiment, the generating the smoothed set of camera
orientation data may include filtering based on a Gaussian
filter.
[0018] In an embodiment, the generating of the smoothed set of
camera orientation data may include filtering based on a temporal
derivative.
[0019] In an embodiment, the set of camera orientation data may
include rotations without any translations.
[0020] In an embodiment, the set of camera orientation data may
include vectors having both rotations and translations.
[0021] In an embodiment, the generating the smoothed set of camera
orientation data is performed by a social networking system.
[0022] In an embodiment, the set of image frames having associated
time stamps and the set of camera orientation data having
associated time stamps may be uploaded to the social networking
system by a user of the social networking system.
[0023] Many other features and embodiments of the invention will be
apparent from the accompanying drawings and from the following
detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates an example pinhole camera model,
according to an embodiment.
[0025] FIG. 2 illustrates a depiction of two example camera
orientations and their corresponding image planes, according to an
embodiment.
[0026] FIG. 3 illustrates a depiction of an example warped image
captured by an RS camera and transformations to correct the image,
according to an embodiment.
[0027] FIG. 4 illustrates an example digital video stabilization
module, according to an embodiment.
[0028] FIG. 5 illustrates graphs of examples of input data and
resulting data after smoothing, according to an embodiment.
[0029] FIG. 6 illustrates an example method for constraint-based
smoothing, according to an embodiment.
[0030] FIG. 7 illustrates an example network diagram of a system
for modifying a set of image frames from a digital video to produce
a stabilized digital video within a social networking system,
according to an embodiment.
[0031] FIG. 8 illustrates an example computer system that may be
used to implement one or more of the embodiments described herein,
according to an embodiment.
[0032] The figures depict various embodiments of the present
invention for purposes of illustration only, wherein the figures
use like reference numerals to identify like elements. One skilled
in the art will readily recognize from the following discussion
that alternative embodiments of the structures and methods
illustrated in the figures may be employed without departing from
the principles of the invention described herein.
DETAILED DESCRIPTION
Digital Video Stabilization and Rolling Shutter Correction using
Gyroscopes
[0033] Rolling shutter correction is a technique for removing image
warping produced by intra-frame camera motion. High-end cameras use
charge-coupled device (CCD) sensors, which have a global shutter
(GS). In a GS camera, including many DSLRs, all pixels on the CCD
sensor are read out and reset simultaneously. Therefore all pixels
collect light during the same time interval. Consequently, camera
motion during the exposure results in some amount of image blur on
these devices. In contrast, low-end cameras typically make use of
complementary metal oxide semiconductor (CMOS) sensors. In
particular, these sensors employ a rolling shutter, where image
rows are read out and reset sequentially. This approach may require
less circuitry compared to CCD sensors and may make CMOS sensors
cheaper to manufacture. For that reason, CMOS sensors are
frequently used in cell phones, music players, and some low-end
camcorders. The sequential readout, however, means that each row is
exposed during a slightly different time window. As a result,
camera motion during row readout will produce a warped image. Fast
moving objects will also appear distorted.
[0034] Image readout in an RS camera is typically in the
millisecond range. Therefore, RS distortions are primarily caused
by high-frequency camera motions. MIS systems could, therefore, be
used to stabilize the camera. While this approach removes rolling
shutter warping, in practice the price range and size of MIS
systems make it not suitable for RS cameras. Some digital rolling
shutter rectification techniques may correct RS artifacts in a
single image, but require user input. In contrast, some embodiments
of the present disclosure may correct RS artifacts for single
images without requiring user input.
[0035] For video, rectifying RS in a sequence of frames using
feature tracking to estimate the camera motion from the video may
present problems. Once the camera motion is known during an RS
exposure, it can be used to rectify the frame. Since this approach
relies on feature trackers, it has the same disadvantages
previously discussed in the case of video stabilization.
[0036] Digital video stabilization techniques may include cropping
or zooming input video frames. This may allow individual frames to
be translated, rotated, or warped to counteract undesired
deformations introduced by hand shake. The amount of cropping may
determine how much leeway (or "wiggle room") is available to remove
these deformations. If, for example, the frame is translated too
far, empty regions (e.g., regions which have no pixel data) may be
visible. Some embodiments of the present disclosure not only smooth
out the camera motion by counteracting hand shake, but may also do
so while preventing empty regions from showing up. It should be
appreciated that other methods for providing the leeway for
stabilization, other than cropping or zooming, may also be
implemented. For example, inpainting techniques may be implemented
to fill empty regions introduced by stabilization. Inpainting may
be used in lieu of, or in addition to, cropping or zooming. For
instance, in an embodiment, a function may be implemented to
determine whether a given deformation results in a frame with all
pixels set (whether by inpainting, zooming, cropping, etc.) to
satisfaction or not.
[0037] Systems and methods are provided for digitally stabilizing
videos by computing smooth camera rotations that satisfy
empty-region prevention constraints. This may enable maximally
smooth camera rotations to be produced for a given crop or zoom
factor.
[0038] The digital video stabilization process may begin, for
example, with video being captured by a camera or device including
a camera, such as a mobile phone, tablet, watch, wearable gear,
etc. The video may include a number of successive image frames that
are captured. The video may be shaky due to the device's size and
weight. The rolling shutter used by sensors in the camera may
produce warping in the output image frames. Gyroscopes may be used
to measure the camera's motions (e.g., rotations) during video
capture. The measured camera motion may be used to stabilize the
video and to rectify the rolling shutter to result in the
stabilized video having output frames with corrected images.
[0039] Techniques of the present disclosure may improve video
quality of RS cameras. In an embodiment, microelectromechanical
systems (MEMS) gyroscopes are implemented to measure camera
rotations. Other gyroscopes and motion sensing devices may also be
implemented. The gyroscopic measurements may be used to perform
video stabilization (e.g., inter-frame motion compensation) and
rolling shutter correction (e.g., intra-frame motion compensation).
This approach may be both computationally inexpensive and robust,
which may make it particularly suitable for real-time
implementations on mobile platforms for instance.
[0040] Systems and methods based on a unified model of a rotating
camera and a rolling shutter may utilize the model to compute a
warp that simultaneously performs rolling shutter correction and
video stabilization. Optimization techniques may be provided that
automatically calibrate the gyroscope and camera. This may permit
the recovery of unknown parameters, such as gyroscope drift and
delay, as well as the camera's focal length and rolling shutter
speed, from a single video and gyroscopic capture. As a result, any
combination of gyroscope and camera hardware may be calibrated
without the need for a specialized laboratory setup. A device
including the camera may also include a motion sensing device, such
as a gyroscope. For example, many smartphones have cameras and
motion sensing devices, such as gyroscopes and accelerometers. In
this way, real-time video stabilization and rolling shutter
correction may be provided without requiring the use of feature
trackers or MIS systems. Furthermore, inexpensive MEMS gyroscopes
may be implemented to measure camera motion directly. Inertial
measurement units (IMUs) may be used for image de-blurring and for
aiding a KLT feature tracker
[0041] Measuring camera motion using motion sensing devices, such
as gyroscopes, permits digital video stabilization and RS
rectification to be performed with high computational efficiency.
This approach may be robust even under poor lighting or substantial
foreground motion, because the video's content is not used for
motion estimation. Furthermore, as stated above, many
camera-enabled mobile phones are already equipped with gyroscopes
or other motion sensing devices. Compared to MIS systems, MEMS
gyroscopes may be significantly less inexpensive, more versatile,
and less bulky.
[0042] In an embodiment, video stabilization may proceed in three
stages: camera motion estimation, motion smoothing, and image
warping. Rolling shutter rectification may proceed in a similar
manner, except the actual camera motion may be used for the warping
computation rather than the smoothed motion. As will be discussed
in further detail herein, both video stabilization and rolling
shutter correction may be performed in one warping computation
under a unified framework.
[0043] In an embodiment, camera motion may be modeled in terms of
rotations only. It should be appreciated that translations may be
measured in addition to, or in place of, rotations in other
embodiments. In some instances, translations may be difficult to
measure accurately using IMUs for example. Moreover, accelerometer
data may require being integrated twice to obtain translations. In
contrast, gyroscopes measure the rate of rotation. Therefore,
gyroscopic data may require only a single integration to obtain the
camera's orientation. As a result, translation measurements may be
significantly less accurate than orientation measurements in some
instances. Furthermore, translation measurements may be complicated
by objects at different depths moving by different amounts. In an
embodiment, stereo or feature-based structure from motion (SfM)
algorithms may be implemented to obtain depth information. Warping
frames in order to remove translations may be performed in some
embodiments, but may be complicated by parallax and occlusions.
[0044] Modeling camera translations in systems may present issues.
For example, an optimizer may fall into a local minimum while
attempting to reconstruct translations from a feature tracker. An
algorithm may assume that the camera is imaging a purely planar
scene (e.g., constant depth). Therefore, translation reconstruction
may be complicated due to unmodeled parallax in the video.
[0045] Embodiments modeling camera rotation only in terms of
rotations, or primarily in terms of rotations, may minimize the
problems encountered with translations. Camera shake and rolling
shutter warping occur primarily from rotations since translations
attenuate quickly with increasing depth, and objects are typically
sufficiently far away from the lens that translational camera
jitter does not produce noticeable motion in the image.
Example Camera Model
[0046] In an embodiment, a rotational rolling shutter camera model
that is based on a pinhole camera model is provided. FIG. 1
illustrates an example pinhole camera model 101, according to an
embodiment. A ray from a camera center c to a point x in the scene
will intersect the image plane at point x. Therefore the projection
of the world onto the image plane depends on the camera's center c,
the focal length f, and the location of the camera's axis (o.sub.x,
o.sub.y) in the image plane. In a pinhole camera the relationship
between image point x in homogeneous coordinates and the
corresponding point X in 3D world coordinates may be specified by
example equation (1).
x=KX, and X=.lamda.K.sup.-1x (1)
Here, .lamda. is an unknown scaling factor and K is the intrinsic
camera. K.sup.-1 may be specified by example equation (2).
K - 1 = ( 1 0 - o x 0 1 - o y 0 0 f ) ( 2 ) ##EQU00001##
(o.sub.x, o.sub.y) is the origin of the camera axis in the image
plane and f is the focal length. The camera's focal length is an
unknown that may be recovered. The camera may be assumed to have
square pixels and the upper diagonal entries set to 1. However,
other embodiments may extend this model to take into account
non-square pixels or other optical distortions.
[0047] Warping may occur from high-frequency camera rotations. For
example, high-frequency camera rotations while the shutter is
rolling from top to bottom may cause the output image to appear
warped. This warped image may be modeled mathematically.
[0048] The world origin may be set to the camera origin. The camera
motion may then be described in terms of its orientation R(t) at
time t. Thus, for any scene point X, the corresponding image point
x at time t may be given by example equation (3).
x=KR(t)X (3)
[0049] The rotation matrices R(t).epsilon. SO(3) may be computed by
compounding the changes in camera angle .DELTA..theta.(t). The
spherical linear interpolation (SLERP) of quaternions may be used
in order to interpolate the camera orientation smoothly and to
avoid gimbal lock. The change in angle between gyroscope samples
may be sufficiently small that Euler angles work as well as
rotation quaternions. .DELTA..theta.(t) may be obtained directly
from gyroscope measured rates of rotation .omega.(t), as specified
in the following example equation (4).
.DELTA..theta.(t)=(.omega.(t+t.sub.d)+.omega..sub.d)*.DELTA.t
(4)
.omega..sub.d is the gyroscope drift and t.sub.d is the delay
between the gryoscope and frame sample timestamps. These parameters
are additional unknowns in that model that may also be
recovered.
[0050] Rolling shutter may also be introduced into the camera
model. In an RS camera, each image row is exposed at a slightly
different time. Camera rotations during this exposure may,
therefore, determine the warping of the image. Translational camera
jitter during rolling shutter exposure does not significantly
impact image warping because objects are typically far away from
the lens. For example, if the camera sways from side to side while
the shutter is rolling, then the output image will be warped as
shown in FIG. 3. The time at which point x was imaged in frame i
depends on how far down the frame it is. It may be determined that
x was imaged at time t(i, y), as specified by the example equation
(5).
t(i,y)=t.sub.i+t.sub.s*y/h, where x=(x,y,1).sup.T (5)
y is the image row corresponding to point x. h is the total number
of rows in the frame. t.sub.i is the timestamp of the i-th frame.
The t.sub.s term indicates that the farther down in a frame, the
longer it took for the rolling shutter to get to that row. Hence,
t.sub.s is the time it takes to read out a full frame going row by
row from top to bottom. A negative t.sub.s value would indicate a
rolling shutter that goes from bottom to top. Automatically
recovering the sign and value of t.sub.s is described in further
detail herein.
[0051] The relationship between image points in a pair of frames
for two different camera orientations may be derived. FIG. 2
illustrates a graphical representation of two camera orientations
and their corresponding image planes, according to an embodiment.
Graphical representation 201 includes two camera orientations 202
and 203. Camera orientation 202 includes image plane i. Camera
orientation 203 includes image plane j. An image of scene point X
appears in the two frames where the ray 211 intersects the image
planes i and j. For a scene point X, the projected points x.sub.i
and x.sub.j in the image plane of two frames i and j, respectively,
may be specified by the following example equations (6).
x.sub.i=KR(t(i,y.sub.i))X, and x.sub.j=KR(t(j,y.sub.j))X (6)
[0052] If these equations are rearranged and if X is substituted
for, a mapping of all points in frame i to all points in frame j is
obtained, as specified by example equation (7).
x.sub.j=KR(t(j,y.sub.j))R.sup.T(t(i,y.sub.i))K.sup.-1x.sub.i
(7)
[0053] While the relationship between two frames have been
described in relation to the same video, in other embodiments, the
frames may be mapped from one camera that rotates according to R(t)
to another camera that rotates according to R'(t). In an
embodiment, both camera centers may be assumed to be at the origin.
The warping matrix W that maps points from one camera to the other
may be specified according to the following example equation
(8).
W(t.sub.1,t.sub.2)=KR'(t.sub.1)R.sup.T(t.sub.2)K.sup.-1 (8)
[0054] Equation 7 may now be specified more compactly according to
the following example equation (9).
x.sub.j=W(t(j,y.sub.j),t(i,y.sub.i))x.sub.i, where R'=R (9)
[0055] W depends on both image rows y.sub.i and y.sub.j of image
points x.sub.i and x.sub.j, respectively. This warping matrix may
be used to match points in frame i to corresponding points in frame
j, while taking the effects of the rolling shutter into account in
both frames.
[0056] This formulation of a warping matrix provides for rolling
shutter correction and video stabilization. A synthetic camera may
be created that has a smooth motion and a global shutter. This
camera's motion may be computed by applying a Gaussian low-pass
filter, for example, to the input camera's motion, which results in
a new set of rotations R'. The rolling shutter duration t.sub.s for
the synthetic camera may be set to 0 as for a global shutter.
W(t.sub.i, t(i, y.sub.i)) may then be computed at each image row
y.sub.i of the current frame i, and the warp may be applied to that
row. The first term of W may now only depend on the frame time
t.sub.i. This operation may map all input frames onto the synthetic
camera, and as a result, simultaneously remove rolling shutter
warping and video shake.
[0057] In certain embodiments, W(t.sub.i, t(i, y.sub.i)) is not
computed for each image row y.sub.i. Instead, the input image may
be subdivided and the warp computed at each vertical subdivision.
FIG. 3 illustrates an example transformation to correct warp,
according to an embodiment. Warped input image frame 301 shows a
subdivided warped image that was captured by an RS camera. The warp
is computed at each vertical subdivision, as shown in image frame
311. Image frame 311 shows a piecewise linear approximation of
non-linear warping. As shown by resulting image frame 316, various
numbers of subdivisions may be sufficient to eliminate artifacts.
For example, in an embodiment, 10 subdivisions may be sufficient to
eliminate visual artifacts. A warped mesh from the input image was
created that is a piecewise linear approximation of the non-linear
warp. While ten subdivisions may be sufficient to remove any
visible RS artifacts, other embodiments may include a different
number of subdivisions. The sampling approach may be referred to as
inverse interpolation. Inverse interpolation may be easy to
implement on a graphical processing unit (GPU) using vertex
shaders. The GPU's fragment shader may take care of resampling the
mesh-warped image using bilinear interpolation. RS warping in
actual videos may not be strong enough to produce aliasing
artifacts due to bilinear inverse interpolation. As a result,
inverse interpolation may work well in practice. Rolling shutter
correction using global image warps may assume that camera rotation
is more or less constant during rolling shutter exposure. A linear
approximation may fail to rectify the rolling shutter, as shown by
image frame 306 in FIG. 3.
Camera and Gyroscope Calibration
[0058] Calibration techniques are provided for recovering the
unknown camera and gyroscope parameters described herein. The
calibration may enable the computation of W directly from the
gyroscope data. The unknown parameters in the model described
herein may include: the focal length of the camera f, the duration
of the rolling shutter t.sub.s, the delay between the gyroscope and
frame sample timestamps t.sub.d, and the gyroscope drift
w.sub.d.
[0059] In some instances, one or more of these parameters, such as
the camera's focal length f, may be specified by the manufacturer.
In some instances, these parameters may be measured experimentally.
For example, a quickly flashing display may be used to measure the
rolling shutter duration t.sub.s. However, these techniques may
tend to be imprecise and error prone. These techniques may also be
tedious. The duration of the rolling shutter may typically be in
the millisecond range. As a result, a small misalignment in t.sub.d
or t.sub.s may cause rolling shutter rectification to fail.
[0060] In an embodiment, these parameters may be estimated from a
single video and gyroscope capture. For example, the user may be
record a video and a gyroscope trace while standing still and
shaking the camera while pointing at a stationary object, such as a
building. The duration of the clip may vary in different
embodiments. In an embodiment, a short clip (e.g., ten seconds or
less in duration) may be sufficient to estimate all the unknown
parameters. This calibration step may only need to be done once for
each camera and gyroscope arrangement.
[0061] In an embodiment, matching points are identified in
consecutive video frames. The matching points may be identified
using, for example, the scale invariant feature transform (SIFT).
Outliers may be discarded using, for example, random sample
consensus (RANSAC). The result may be a set of point
correspondences x.sub.i and x.sub.j for all neighboring frames in
the captured video. Given this ground truth, calibration may be
formulated as an optimization problem where the mean-squared
re-projection error of all point correspondences may be minimized.
This is specified in the following example equation (10).
J = ( i , j ) x j - W ( t ( j , y j ) , t ( i , y i ) ) x i 2 ( 10
) ##EQU00002##
[0062] A number of non-linear optimizers may be used to minimize
the objective function. Coordinate descent by direct objective
function evaluation may converge quickly, and is implemented in one
embodiment. Each time a step is taken where the objective function
J does not decrease; the step direction is reversed and the step
size of the corresponding parameter is decreased. The algorithm may
terminate when the step size for all parameters drops below a
desired threshold, such as when a target precision is achieved. The
convergence may occur quickly in some instances. For example, in
one embodiment, the convergence may occur in 2 seconds or less for
a calibration video of about 10 seconds in duration.
[0063] In an embodiment, the optimization may be initialized by
setting the focal length such that the camera has a field of view
of 45.degree.. All other parameters may be set to 0. With these
initial conditions, the optimizer may converge to the correct
solution for the dataset. More generally, falling into a local
minimum (e.g., when the delay between the gyroscope and frame
timestamps is large) may be avoided by restarting the coordinate
descent algorithm for a range of plausible parameters, and
selecting the best solution. The average re-projection error for
correctly recovered parameters may be, for example, around 1
pixel.
[0064] An additional unknown in the model may be the relative
orientation of the gyroscope to the camera. For example, rotations
about the gyro's y-axis may correspond to rotations about the
camera's x-axis.
[0065] To discover the gyroscope orientation, the 3 rotation axes
may be permuted and the optimizer may be run for each permutation.
The permutation that minimizes the objective best may correspond to
the camera's axis ordering. The re-projection error may be
significantly larger for incorrect permutations. Therefore, this
method may work well in practice.
[0066] While it has been assumed that the camera has a vertical
rolling shutter, the RS model may be easily modified to work for
image columns instead of rows. Finding the minimum re-projection
error for both cases may indicate whether the camera has a
horizontal or vertical rolling shutter.
[0067] Finally, the results achieved by calibration may be
demonstrated by analyzing the video and gyroscope signals before
and after calibration. Assuming rotations between consecutive
frames are small, the translations in the image may be
approximately computed from rotations as specified in the following
example equation (11).
x . ( t ) .apprxeq. f * .omega. ^ ( t + t d ) , where { x . = ( x .
, y . ) T .omega. ^ = ( .omega. y , .omega. x ) T ( 11 )
##EQU00003##
[0068] Equation (11) assumes there are no effects due to rolling
shutter (e.g., t.sub.s=0), and rotations about the z-axis (e.g.,
.omega..sub.z) may be ignored. {dot over (x)} is the average rate
of translation along x and y for all point correspondences in
consecutive frames. If the optimizer converged to the correct focal
length f and gyroscope delay t.sub.d, then the two signals should
align. Before calibration, the amplitudes of the signals x and
f*.omega.y(t+t.sub.d) do not match because the initial estimate for
f is too low. The signals may be shifted when t.sub.d is
initialized to 0. After calibration, the signals may be well
aligned because accurate focal length and gyroscope delay have been
recovered. Precise gyroscopes, such as MEMS gyroscopes, enable the
gyroscope data to match the image motions, resulting in the
improved video stabilization and rolling shutter correction.
Constraint-Based Rotation Smoothing
[0069] In some aspects of the present disclosure, system and
methods may be provided for computing an optimally smooth camera
motion under the constraint that empty regions are not visible, or
below a minimum threshold value. FIG. 4 illustrates an example
digital video stabilization module, according to an embodiment.
Digital video stabilization module 400 is shown including an input
module 401, a smoothing module 402, and a warping module 403.
[0070] Input module 401 may provide inputs to be stabilized the
smoothing module 402 and the warping module 405. Input module 401
may receive the inputs associated with the video that is to be
stabilized. For example, inputs may include a set of N frames
F.sub.i, corresponding times t.sub.i for the N frames F.sub.i, and
camera orientations .theta..sub.i, where i={1 . . . N}.
[0071] Smoothing module 402 computes a set of new smoothed camera
orientations .phi..sub.i, such that a constraint function f(.phi.,
t) is satisfied. Smoothing module 402 may include rate of rotation
module 403 and constraint determination module 404.
[0072] Rate of rotation module 403 computes the rate of rotation to
ensure a sufficiently small rate of rotation is maintained for the
generation of smooth camera orientations. Constraint determination
module 404 determines whether a constraint is met for target
orientations .phi..sub.i at time t.sub.i. For example, in one
embodiment, the constraint function f(.phi.,t) may return 1 or 0
depending on whether empty regions are visible or not,
respectively, given a target orientation .phi..sub.i at time
t.sub.i.
[0073] For example, the constraint determination module 404 may
determine whether a minimal amount of empty regions (e.g., below a
threshold amount) are produced in successive image frames. If the
amount of empty regions falls below the threshold amount, then the
constraint is met (e.g., the amount of empty regions does not
exceed the threshold amount), and the target orientation .phi. and
its corresponding time t may be used to generate a smooth
orientation that has a sufficiently small rate of rotation that
does not generate an amount of empty spaces above a threshold
value. If the constraint is not met (e.g., the amount of empty
regions exceeds the threshold amount), then the corresponding
target orientation .phi. may be adjusted to maintain a sufficiently
small rate of rotation while satisfying the constraint. In an
embodiment, the threshold amount of empty regions is zero. In
another embodiment, the threshold amount of empty regions is
approximately zero or a negligible value that is determined to be
undetectable by the human eye. In yet another embodiment, the
threshold amount of empty regions is a value that prevents
cropping, zooming, or inpainting to be used effectively, such as to
eliminate all empty regions, or approximately all empty regions. In
other embodiments, the threshold amount of empty regions may be set
as desired based on the application and level of tolerance.
[0074] Warping module 405 generates warped frames based on the set
of new smoothed camera orientations .phi..sub.i computed by the
smoothing module 402. For example, the warping module 405 may
implement a warping function g(F, .phi., t) that takes as input a
frame F, a smoothed orientation .phi. and its corresponding time t,
and generates a warped frame F'. Given the smoothly varying
.phi..sub.i over t.sub.i as output by the smoothing module 402, and
appropriate choices of functions f and g, the resulting warped
frames F'.sub.i will compose a stabilized output video. The
function f may depend on the choice of warping function g, and may
simply indicate whether, after applying the warping function g,
empty regions would be visible in the frame or not.
[0075] The specific warping function implemented may vary in
different embodiments. Different warping functions may be
appropriate for various cameras or desired approximations. For
example, the warping function implemented may be based on whether a
camera has a rolling shutter and minor lens aberrations or whether
it has a global shutter. For instance, in one embodiment, for
cameras with a global shutter, a homography warping function may be
implemented. Other approximations, such as affine transformations,
or a rotation plus a translation in the frame's image space may be
implemented.
[0076] In an embodiment, the .theta..sub.i input are rotations in
the SO(3) group. There are a variety of ways to represent
rotations, such as by rotation matrixes and quaternions.
Representations that lie in SO(3) may be converted into a
representation that facilitates smooth interpolation, such as
quaternions rather than Euler angles. The .theta..sub.i rotations
may be computed from an image-based feature tracker, for example,
or by directly measuring and integrating gyroscope readings. Any
other method that produces accurate estimates of the camera's
orientation may be implemented in other embodiments.
[0077] While .phi. has been described in terms of camera rotations,
in other embodiments .theta. may include a vector that holds both
rotations and translations of the camera in 3D space. For instance,
vectors that include both rotations and translations may be
produced by a structure from motion algorithm. In an embodiment,
.theta. may include translations or rotations in the frame's image
space, or other less accurate but potentially computationally
cheaper approximations. As long as .theta. can be smoothly
interpolated and the resulting .phi. can be input to a
corresponding f and g function, the digital video stabilization may
be achieved.
[0078] The phrase "smooth camera motion" may be used herein to
refer to small changes in the rate of rotation. This is
distinguished from small changes in rotation of neighboring frames.
Small changes in the rate of rotation may produce orientations that
ease in and out of imposed constraints over time. Small changes in
rotation of neighboring frames interpolates to and from the
constraints while producing discontinuities in orientation
derivatives at the time where the constraint is enforced.
[0079] The constraint-based rotation smoothing may include an
optimization that includes minimizing an energy function based on
rate of rotation and the constraint.
[0080] In an embodiment, the energy function, J, to be minimized
may be specified by the following example equation (12).
J = i = 2 N - 1 .phi. i + 1 - .phi. i t i + 1 - t i - .phi. i -
.phi. i - 1 t i - t i - 1 2 s . t . f ( .phi. i , t i ) = 0
.A-inverted. i ( 12 ) ##EQU00004##
[0081] The rotations .phi. may be represented as unit quaternions
(also known as versors). Furthermore, the hard constraint may be
replaced with a soft constraint, as specified in the following
example equation (13).
J = i = 2 N - 1 .phi. i + 1 - .phi. i t i + 1 - t i - .phi. i -
.phi. i - 1 t i - t i - 1 2 + .lamda. i = 1 N f ( .phi. i , t i ) (
13 ) ##EQU00005##
.lamda. may determine how strongly the f constraint is enforced.
For example, setting .lamda. to infinity may ensure that no empty
regions are visible, assuming the constraints may be satisfied.
[0082] A variety of optimization algorithms may be used to minimize
the energy function J in either the form shown in example equation
(12) or (13). In an embodiment, an iterative algorithm based on
gradient descent of example equation (12) is implemented, where the
constraint may be enforced at each iteration. In an embodiment, the
frames may be equally spaced temporally, such as a camera that
records at a specific number of frames per second. With equally
spaced frames, the denominator may be assumed to be constant and
may then be taken out of the sum. The derivative may then specified
by the following example equation (14).
.differential. J .differential. .phi. i = C ( .phi. i + 2 - 4 .phi.
i + 1 + 6 .phi. i - 4 .phi. i - 1 + .phi. i - 2 ) , ( 14 )
##EQU00006##
[0083] C may be a constant that controls the magnitude of the
gradient. In some embodiments, this may be picked automatically by
some forms of gradient descent, such as momentum-based methods. In
other embodiments, this may be set as desired to control the rate
of descent in plain gradient descent. An example value may be, for
instance, C=2/(.DELTA.t).sup.2. Equation (14) may be specified more
compactly by the following example equation (15).
.differential. J .differential. .phi. i = CK .PHI. i , where K = [
1 - 4 6 - 4 1 ] T , and .PHI. i = [ .phi. i + 2 T .phi. i + 1 T
.phi. i T .phi. i - 1 T .phi. i - 2 T ] ( 15 ) ##EQU00007##
[0084] The kernel K may be a Laplacian of Gaussian (LoG) filter.
The LoG filter may be approximated with a Difference of Gaussians
(DoG) or Difference of Boxes (DoB) filter. The kernel K may also be
adjusted by convolving a LoG filter with a Gaussian filter. This
may control how gradually the rate of rotation should change (or
the amount of easing in and out of constraints). The choices of the
LoG/DoG/DoB and/or Gaussian filters may affect the coefficients and
size of kernel K, but as long as the kernel computes a form of a
temporal derivative, the optimized orientations may exhibit some
form of easing in and out of the constraints.
[0085] In an embodiment, the applying of the kernel to the
quaternions is doing linear weighting of the 4D vectors. In theory,
interpolating quaternions using spherical linear interpolation
(slerp) may be an accurate method. For small changes in angles,
linear interpolation plus a normalization of the resulting
quaternion (lerp) at each iteration is sufficient to produce
sufficiently accurate results. Such results may be achieved because
sin(.theta.).apprxeq..theta. when .theta. is small. The change in
angle induced by handshake (e.g., changes that are to be rectified)
are typically not large. Furthermore, reasonable levels of
cropping, zooming, or inpainting factors may not leave much leeway.
Only small angles may not produce empty regions. Thus, the angle
induced by handshake between quaternions of consecutive
orientations may not be large in practice, and the approximation
may be both accurate and computationally efficient. Furthermore,
for rapid camera rotations (e.g., the user quickly panning left),
the constraint function f may dominate the resulting orientations.
Thus, any inaccuracies from lerp may not be noticeable.
[0086] In an embodiment, the constraint-based rotation smoothing
may be specified in terms of the following example algorithm
(1).
TABLE-US-00001 Algorithm 1 Constraint-Based Rotation Smoothing for
i = 1..N do .phi..sub.i .rarw. .theta..sub.i end for for j =
1..numiter do for i = 3..(N - 2) do if f(n(.phi..sub.i -
CK.PHI..sub.i), t.sub.i) = 0 then .phi..sub.i .rarw. n(.phi..sub.i
- CK.PHI..sub.i) end if end for end for
.phi..sub.i may be precomputed in the outer loop, such that it does
not change in the inner loop. The number of iterations, "numiter",
may be set sufficiently high to result in smooth rotations. The
resulting .phi..sub.i may then be fed into g to produce a
stabilized output video.
[0087] n(.phi.) is the normalization step in lerp and may be
defined as: n(.phi.)=.phi./.parallel..phi..parallel.. The indexing
i in algorithm 1 is selected such that .phi..sub.i is valid, and
therefore may depend on the size of the kernel K. In this example,
the rotations at the boundaries may be held fixed. In other
embodiments, the boundary may be extended via extrapolation,
allowing for the entire set of orientations to be iterated over
during optimization. The entire set of orientations may be
specified as the following set.
{.phi..sub.i}.sub.i=1.sup.N
[0088] FIG. 5 illustrates graphs of examples of input data and
resulting data after smoothing, according to an embodiment. The top
graph includes input data 502 plotted over time with constraints
503 denoted by circles. The bottom graph includes resulting data
504, including constraints 503, that resulted from the input data
502 being smoothed in accordance with the constraint-based rotation
smoothing techniques described herein. For example, the resulting
data 504 may be smoothed by enforcing the rate of rotation (or
derivative) to be small (or below a threshold value) while ensuring
that the constraint (e.g., a threshold amount of empty regions are
not produced in successive image frames) is met. Small changes in
the rate of rotation may produce orientations that ease in and out
of imposed constraints over time. The resulting data 504 eases in
and out of the constraints 503. On the other hand, the middle graph
includes resulting data 506, including constraints 503, that
resulted from an attempted smoothing of the input data 502 by
enforcing the change in orientation of neighboring frames to be
small. Small changes in rotation of neighboring frames interpolates
to and from the constraints while producing discontinuities in
orientation derivatives at the time where the constraint is
enforced. As shown, the resulting data 506 includes discontinuities
in the derivative at the constraints 503.
[0089] FIG. 6 illustrates an example method for constraint-based
smoothing, according to an embodiment. At block 601 of method 600,
video data is received. The video data may include a set of image
frames having associated time stamps. In an embodiment, block 601
may be performed by input module 701 of FIG. 4.
[0090] At block 603, camera orientation data having associated time
stamps are received. For example, the device including the camera
may also include an orientation sensor, such as a gyroscope,
accelerometer, etc., that generates camera orientation data that
tracks the orientation of the camera during the capture of the
video. The camera orientation data may include associated time
stamps to link or otherwise associate the camera orientation data
to the set of images in the video data. In some instances, the
camera orientation data may be received at the same time as the
video data, such as together with the video data. In an embodiment,
block 602 may be performed by input module 701 of FIG. 4.
[0091] In one embodiment, blocks 601 and 603 may be performed by
the device having the camera (e.g., smartphone or other handheld
device) that is used to capture the video. For example, the video
data and camera orientation data may be received upon capture of
the video. In another embodiment, blocks 601 and 603 may be
performed by a separate device (e.g., computer) that subsequently
receives the video data captured by the device including the camera
(e.g., smartphone). For example, the video data and camera
orientation data may be transmitted or uploaded to a separate
device from the device including the camera and orientation sensor,
such as a smartphone with camera.
[0092] At block 605, a set of smoothed camera orientation data is
generated by minimizing the rate of rotation between successive
images frames while minimizing (or limiting) the amount of
resulting empty regions in a resulting set of smoothed image
frames. The resulting set of smoothed image frames are reoriented
based on the smoothed set of camera orientation data.
[0093] In an embodiment, the set of smoothed camera orientation
data is generated by minimizing either equations (12) or (13)
described herein. In an embodiment, an iterative algorithm based on
gradient descent of example equation (12) is implemented, where the
constraint may be enforced at each iteration.
[0094] At block 607, the set of image frames are warped to form a
set of corrected image frames. The set of image frames may be
warped based on the associated time stamps for the set of image
frames and the smoothed set of camera orientation data. In an
embodiment, an individual image frame may be divided into a
plurality of subsections, with each subsection having an associated
time stamp and camera orientation. Each subsection may be realigned
based on the associated time stamp and camera orientation to form
an individual corrected image frame.
Reducing Visibility of Motionblur Artifacts
[0095] Digital video stabilization of video taken in low light
often produces strange motion blur artifacts. This may occur
because motion blur looks strange when the motion (e.g., handshake)
that caused it is removed. In some instances, it may be necessary
to leave just enough of the handshake in the stabilized video to
explain the motion trails. If there is a clear horizontal motion
trail in a frame, it may be necessary for the orientation to change
horizontally according to that trail in order to for the trail to
make sense. If there is no horizontal motion, then that trail may
appear to pop in and out for no reason in the stabilized video,
which can cause visible motion blur artifacts.
[0096] In an embodiment, the change in orientation
.DELTA..theta..sub.i that occurred while the camera's shutter was
open is computed according to the following example equation
(16).
.DELTA..theta..sub.i=.theta.(t.sub.i.sup.s)-.theta.(t.sub.i.sup.s+e.sub.-
i) (16)
t.sub.i.sup.s may represent the time at which the shutter opened
for frame F.sub.i. e.sub.i is the frame's exposure duration.
.theta.(t) is the camera's orientation at time t, which may be
computed by interpolating over the following expression.
{.theta..sub.i,t.sub.i}.sub.i=1.sup.N
[0097] In the example described above for digital video
stabilization and rolling shutter correction using gyroscopes,
.DELTA..theta..sub.i may also be computed directly from the
gyroscope readings by only integrating over the period where the
shutter is open. The sum inside equation (1) or equation (2) may be
modified as specified in the following example equation (17).
i = 2 N - 1 .phi. i + 1 - .phi. i t i + 1 - t i - .phi. i - .phi. i
- 1 t i - t i - 1 - ( .DELTA. .theta. i - .DELTA. .theta. i - 1 ) 2
( 17 ) ##EQU00008##
[0098] Equation (17) assumes that t.sub.i.sup.s.gtoreq.t.sub.i and
t.sub.i.sup.s+e.sub.i.ltoreq.t.sub.i+1. The shutter does not open
before the timestamp of the frame, and closes prior to the start of
the next frame. In another embodiment, the input time stamps may be
calculated differently (e.g., t.sub.i is the time when the shutter
closed) and a preprocessing step may be added to adjust the
timestamps to meet the requirements.
[0099] In the embodiment described above, changes in orientation
that left motion trails in the frames are preserved. In another
embodiment, an approximation may be implemented as specified by the
following example equation (18).
i = 2 N - 1 .phi. i + 1 - .phi. i t i + 1 - t i - .phi. i - .phi. i
- 1 t i - t i - 1 2 + .gamma. i = 1 N - 1 .phi. i + 1 - .phi. i t i
+ 1 - t i - .DELTA. .theta. i 2 ( 18 ) ##EQU00009##
[0100] The approximation in equation (18) may attempt to optimize
.phi.i such that orientation changes fall along motion trails
.DELTA..theta..sub.i. The .gamma. scaling factor may control the
tradeoff between smoothness and how closely the motion trails
should be followed.
Selecting a Good Zoom Factor
[0101] If, for example, a tolerable zoom factor (or crop factor,
inpainting factor, or any other measure applicable to the algorithm
used to provide leeway for digital video stabilization) is between
1 and 1.25.times.. For a given video, it may be desirable to
determine the smallest zoom factor that will provide enough leeway
to produce smooth camera motions. In an embodiment, the smoothness
of the resulting camera motion may be measured by the following
example equation (19).
q = 1 N - 2 i = 2 N - 1 f ( n ( .phi. i - CK .PHI. i ) , t i ) ( 19
) ##EQU00010##
In equation (19), q measures how frequently the empty region
constraint is enforced. For example, a value of q=0.1 may mean that
on average f is enforced every 10 frames in order to prevent empty
regions from showing through. If, for example, a spacing of 20
frames is desired for easing in and out of constraints, then a good
value may be q=0.05.
[0102] To find the zoom factor z' that provides a desired q' value,
algorithm 1 may be solved for a range of zoom factors (say:
z.epsilon.[1, 1.05, 1.1, 1.15, 1.2, 1.25]). Given a zoom factor z
and the resulting .phi..sub.i's obtained by running algorithm 1,
the resulting q value may be computed from equation (19). The zoom
factor that provided the closest q to q' may then be selected. In
another embodiment, the zoom factor z' may be found by linearly
interpolating the resulting dataset (q, z) at q'. The (q, z) lookup
table for typical hand-held recordings may also be precomputed and
q' estimated from the median or mean rate of rotation. This
approach may be less accurate for a particular video, but it may be
faster because it doesn't require running the optimization
algorithm multiple times.
Improving Computational Efficiency
[0103] There are a number of ways to improve the efficiency of
algorithm (1), such as introducing approximations, using optimizers
other than gradient descent, etc. In one embodiment, the size of
the kernel in K in equation (15) may be reduced and the gradient
may be updated as specified in the following example equation
(20).
.differential. J .differential. .phi. i = C ( 2 K .PHI. i - K .PHI.
i - 1 - K .PHI. i + 1 ) , where K = [ - 1 2 - 1 ] T ( 20 )
##EQU00011##
[0104] By reducing the size of the kernel (and reusing it), the
computation of the gradient may be effectively sped up. Another
property of the kernel in equation (20) is that the value of
K.phi.i may be computed more accurately using slerp. This may be
done over non-uniformly spaced frames as specified in the following
example equation (21).
.differential. .phi. i = .phi. i - slerp ( .phi. i - 1 , .phi. i +
1 , t i - t i - 1 t i + 1 - t i - 1 ) ( 21 ) ##EQU00012##
[0105] Even more accurately, the spherical tangent formed by .phi.i
and slerp may be determined and used in equation (20). The
spherical tangent formed by .phi.i and slerp may be specified in
the following example expression.
.phi. i and slerp ( .phi. i - 1 , .phi. i + 1 , t i - t i - 1 t i +
1 - t i - 1 ) ##EQU00013##
[0106] In another embodiment, efficiency may be improved by
improving the rate of convergence of algorithm 1 described herein.
This may be achieved by running it in coarse to fine mode. For
example, algorithm 1 may be initialized by supplying and solving
for every 16th orientation .phi..sub.i. Linear or cubic
interpolation (e.g., slerp or squad) may then be used to compute
the .phi..sub.i in between. A value for every 8th orientation is
obtained. Algorithm 1 may be run again, but now optimizing every
8th orientation for smoothness and constraints. This may be
repeated until algorithm 1 has been run over every orientation.
[0107] Running coarse to fine may permit algorithm 1 to be run for
significantly fewer iterations at each step. The overall camera
motion may be smoothed out and then the orientations may be refined
to meet constraints at increasingly smaller frame intervals while
still remaining smooth. In another embodiment, non-uniform sampling
may be used. For example, instead of picking every 16th frame,
frames may be picked based on how far the orientation has deviated
from the previously picked frame. The segments may then be
subdivided until a smoothed orientation has been computed for all
frames.
[0108] Since coarser or non-uniform sampling may introduce larger
consecutive changes in orientations, using the slerp modification
presented in equation (21) may produce more accurate results.
Example Applications to Real-Time Stabilization
[0109] The following is provided as an example embodiment of
adopting the algorithm to real-time settings. With N frames kept in
memory, the algorithm is run in a sliding window fashion. Index i
may denote the start of the sliding window, and i+N may denote the
end. Orientations inside the sliding window may be malleable in
that they may be updated by running the algorithm. These
orientations may be specified by the following set (2).
{.phi..sub.j}.sub.j=i.sup.i+N
[0110] Orientations preceding the sliding window (e.g.,
.phi..sub.i-1) may be fixed. The starting orientation may be
.phi..sub.i-1 and the rate of rotation (e.g., as measured by the
gyroscope or computed from a feature tracker) may be integrated to
obtain orientations {.theta..sub.i, .theta..sub.i+1, . . . ,
.theta..sub.i+N}. This may be used as input for the optimization
algorithm and compute {.phi..sub.i, .phi..sub.i+1, . . . ,
.phi..sub.i+N-2}. The orientations {.phi..sub.i-2, .phi..sub.i-1}
and {.phi..sub.i+N-1=.theta..sub.i+N-1,
.theta..sub.i+N=.theta..sub.i+N} may be held fixed and may serve as
the boundary conditions that ensure that motions are smooth going
into and out of the sliding window.
[0111] Once the algorithm is run, the orientation of .phi..sub.i,
which may be used to warp frame F.sub.i, may be obtained. Once the
frame has been warped, it may be passed along to the encoder and
removed from the buffer of N frames. A new frame may then be
received from the camera and the sliding window may be advanced by
one frame.
[0112] The procedure may be repeated until the recording stops and
all frames have been processed. For the very first frame, i=1,
{.phi..sub.-1, .phi..sub.0} may be undefined. .phi..sub.-1 and
.phi..sub.0 may be set to the identity quaternion. Once the last
frame is received, the buffer may be flushed by using the
orientations computed inside the final sliding window to warp their
respective frames.
[0113] In some instances, a small buffer size (e.g., N=5) may not
allow an easing in and out of constraints. In such cases, it may be
necessary to modify the constraint function f to be a soft
constraint that ramps up to a hard constraint. This may be referred
to as function f'(.phi., t). Instead of returning 0 or 1, f'
returns a new orientation .phi.', that may be pushed away from the
frame border. The closer orientation .phi. comes to showing an
empty region, the more f' may push the resulting .phi.' away from
the empty region. Algorithm 1 may then be reformulated as specified
in the following example algorithm (2).
TABLE-US-00002 Algorithm 2 Soft Constraint-Based Rotation Smoothing
for i = 1..N do .phi..sub.i .rarw. .theta..sub.i end for for j =
1..numiter do for i = 3..(N - 2) do .phi..sub.i .rarw.
f'(n(.phi..sub.i - CK.PHI..sub.i), t.sub.i) end for end for
[0114] Note that if f' simply returns .phi..sub.i when orientation
n(.phi..sub.i-CK.phi..sub.i) results in empty regions, then
algorithms 1 and 2 may be equivalent. The optimization rate of
algorithm 1 may be improved by using algorithm 2, with a function
f' that slerps .phi.i towards n(.phi..sub.i-CK.phi..sub.i) but
stops just at the point where empty regions are about to
appear.
Social Networking System--Example Implementation
[0115] FIG. 7 is a network diagram of an example system 700 for
estimating user attention on a website or application in accordance
with an embodiment of the invention. The system 700 includes one or
more user devices 710, one or more external systems 720, a social
networking system 730, and a network 750. In an embodiment, the
social networking system discussed in connection with the
embodiments described above may be implemented as the social
networking system 730. For purposes of illustration, the embodiment
of the system 700, shown by FIG. 7, includes a single external
system 720 and a single user device 710. However, in other
embodiments, the system 700 may include more user devices 710
and/or more external systems 720. In certain embodiments, the
social networking system 730 is operated by a social network
provider, whereas the external systems 720 are separate from the
social networking system 730 in that they may be operated by
different entities. In various embodiments, however, the social
networking system 730 and the external systems 720 operate in
conjunction to provide social networking services to users (or
members) of the social networking system 730. In this sense, the
social networking system 730 provides a platform or backbone, which
other systems, such as external systems 720, may use to provide
social networking services and functionalities to users across the
Internet.
[0116] The user device 710 comprises one or more computing devices
that can receive input from a user and transmit and receive data
via the network 750. In one embodiment, the user device 710 is a
conventional computer system executing, for example, a Microsoft
Windows compatible operating system (OS), Apple OS X, and/or a
Linux distribution. In another embodiment, the user device 710 can
be a device having computer functionality, such as a smart-phone, a
tablet, a personal digital assistant (PDA), a mobile telephone,
etc. The user device 710 is configured to communicate via the
network 750. The user device 710 can execute an application, for
example, a browser application that allows a user of the user
device 710 to interact with the social networking system 730. In
another embodiment, the user device 710 interacts with the social
networking system 730 through an application programming interface
(API) provided by the native operating system of the user device
710, such as iOS and ANDROID. The user device 710 is configured to
communicate with the external system 720 and the social networking
system 730 via the network 750, which may comprise any combination
of local area and/or wide area networks, using wired and/or
wireless communication systems.
[0117] In one embodiment, the network 750 uses standard
communications technologies and protocols. Thus, the network 750
can include links using technologies such as Ethernet, 802.11,
worldwide interoperability for microwave access (WiMAX), 3G, 4G,
CDMA, GSM, LTE, digital subscriber line (DSL), etc. Similarly, the
networking protocols used on the network 750 can include
multiprotocol label switching (MPLS), transmission control
protocol/Internet protocol (TCP/IP), User Datagram Protocol (UDP),
hypertext transport protocol (HTTP), simple mail transfer protocol
(SMTP), file transfer protocol (FTP), and the like. The data
exchanged over the network 750 can be represented using
technologies and/or formats including hypertext markup language
(HTML) and extensible markup language (XML). In addition, all or
some links can be encrypted using conventional encryption
technologies such as secure sockets layer (SSL), transport layer
security (TLS), and Internet Protocol security (IPsec).
[0118] In one embodiment, the user device 710 may display content
from the external system 720 and/or from the social networking
system 730 by processing a markup language document 714 received
from the external system 720 and from the social networking system
730 using a browser application 712. The markup language document
714 identifies content and one or more instructions describing
formatting or presentation of the content. By executing the
instructions included in the markup language document 714, the
browser application 712 displays the identified content using the
format or presentation described by the markup language document
714. For example, the markup language document 714 includes
instructions for generating and displaying a web page having
multiple frames that include text and/or image data retrieved from
the external system 720 and the social networking system 730. In
various embodiments, the markup language document 714 comprises a
data file including extensible markup language (XML) data,
extensible hypertext markup language (XHTML) data, or other markup
language data. Additionally, the markup language document 714 may
include JavaScript Object Notation (JSON) data, JSON with padding
(JSONP), and JavaScript data to facilitate data-interchange between
the external system 720 and the user device 710. The browser
application 712 on the user device 710 may use a JavaScript
compiler to decode the markup language document 714.
[0119] The markup language document 714 may also include, or link
to, applications or application frameworks such as FLASH.TM. or
Unity.TM. applications, the SilverLight.TM. application framework,
etc.
[0120] In one embodiment, the user device 710 also includes one or
more cookies 716 including data indicating whether a user of the
user device 710 is logged into the social networking system 730,
which may enable modification of the data communicated from the
social networking system 730 to the user device 710.
[0121] The external system 720 includes one or more web servers
that include one or more web pages 722a, 722b, which are
communicated to the user device 710 using the network 750. The
external system 720 is separate from the social networking system
730. For example, the external system 720 is associated with a
first domain, while the social networking system 730 is associated
with a separate social networking domain. Web pages 722a, 722b,
included in the external system 720, comprise markup language
documents 714 identifying content and including instructions
specifying formatting or presentation of the identified
content.
[0122] The social networking system 730 includes one or more
computing devices for a social network, including a plurality of
users, and providing users of the social network with the ability
to communicate and interact with other users of the social network.
In some instances, the social network can be represented by a
graph, i.e., a data structure including edges and nodes. Other data
structures can also be used to represent the social network,
including but not limited to databases, objects, classes, meta
elements, files, or any other data structure. The social networking
system 730 may be administered, managed, or controlled by an
operator. The operator of the social networking system 730 may be a
human being, an automated application, or a series of applications
for managing content, regulating policies, and collecting usage
metrics within the social networking system 730. Any type of
operator may be used.
[0123] Users may join the social networking system 730 and then add
connections to any number of other users of the social networking
system 730 to whom they desire to be connected. As used herein, the
term "friend" refers to any other user of the social networking
system 730 to whom a user has formed a connection, association, or
relationship via the social networking system 730. For example, in
an embodiment, if users in the social networking system 730 are
represented as nodes in the social graph, the term "friend" can
refer to an edge formed between and directly connecting two
users.
[0124] Connections may be added explicitly by a user or may be
automatically created by the social networking system 730 based on
common characteristics of the users (e.g., users who are alumni of
the same educational institution). For example, a first user
specifically selects a particular other user to be a friend.
Connections in the social networking system 730 are usually in both
directions, but need not be, so the terms "user" and "friend"
depend on the frame of reference. Connections between users of the
social networking system 730 are usually bilateral ("two-way"), or
"mutual," but connections may also be unilateral, or "one-way." For
example, if Bob and Joe are both users of the social networking
system 730 and connected to each other, Bob and Joe are each
other's connections. If, on the other hand, Bob wishes to connect
to Joe to view data communicated to the social networking system
730 by Joe, but Joe does not wish to form a mutual connection, a
unilateral connection may be established. The connection between
users may be a direct connection; however, some embodiments of the
social networking system 730 allow the connection to be indirect
via one or more levels of connections or degrees of separation.
[0125] In addition to establishing and maintaining connections
between users and allowing interactions between users, the social
networking system 730 provides users with the ability to take
actions on various types of items supported by the social
networking system 730. These items may include groups or networks
(i.e., social networks of people, entities, and concepts) to which
users of the social networking system 730 may belong, events or
calendar entries in which a user might be interested,
computer-based applications that a user may use via the social
networking system 730, transactions that allow users to buy or sell
items via services provided by or through the social networking
system 730, and interactions with advertisements that a user may
perform on or off the social networking system 730. These are just
a few examples of the items upon which a user may act on the social
networking system 730, and many others are possible. A user may
interact with anything that is capable of being represented in the
social networking system 730 or in the external system 720,
separate from the social networking system 730, or coupled to the
social networking system 730 via the network 750.
[0126] The social networking system 730 is also capable of linking
a variety of entities. For example, the social networking system
730 enables users to interact with each other as well as external
systems 720 or other entities through an API, a web service, or
other communication channels. The social networking system 730
generates and maintains the "social graph" comprising a plurality
of nodes interconnected by a plurality of edges. Each node in the
social graph may represent an entity that can act on another node
and/or that can be acted on by another node. The social graph may
include various types of nodes. Examples of types of nodes include
users, non-person entities, content items, web pages, groups,
activities, messages, concepts, and any other things that can be
represented by an object in the social networking system 730. An
edge between two nodes in the social graph may represent a
particular kind of connection, or association, between the two
nodes, which may result from node relationships or from an action
that was performed by one of the nodes on the other node. In some
cases, the edges between nodes can be weighted. The weight of an
edge can represent an attribute associated with the edge, such as a
strength of the connection or association between nodes. Different
types of edges can be provided with different weights. For example,
an edge created when one user "likes" another user may be given one
weight, while an edge created when a user befriends another user
may be given a different weight.
[0127] As an example, when a first user identifies a second user as
a friend, an edge in the social graph is generated connecting a
node representing the first user and a second node representing the
second user. As various nodes relate or interact with each other,
the social networking system 730 modifies edges connecting the
various nodes to reflect the relationships and interactions.
[0128] The social networking system 730 also includes
user-generated content, which enhances a user's interactions with
the social networking system 730. User-generated content may
include anything a user can add, upload, send, or "post" to the
social networking system 730. For example, a user communicates
posts to the social networking system 730 from a user device 710.
Posts may include data such as status updates or other textual
data, location information, images such as photos, videos, links,
music or other similar data and/or media. Content may also be added
to the social networking system 730 by a third party. Content
"items" are represented as objects in the social networking system
730. In this way, users of the social networking system 730 are
encouraged to communicate with each other by posting text and
content items of various types of media through various
communication channels. Such communication increases the
interaction of users with each other and increases the frequency
with which users interact with the social networking system
730.
[0129] The social networking system 730 includes a web server 732,
an API request server 734, a user profile store 736, a connection
store 738, an action logger 740, an activity log 742, an
authorization server 744, and a digital video stabilization module
746. In an embodiment of the invention, the social networking
system 730 may include additional, fewer, or different components
for various applications. Other components, such as network
interfaces, security mechanisms, load balancers, failover servers,
management and network operations consoles, and the like are not
shown so as to not obscure the details of the system.
[0130] The user profile store 736 maintains information about user
accounts, including biographic, demographic, and other types of
descriptive information, such as work experience, educational
history, hobbies or preferences, location, and the like that has
been declared by users or inferred by the social networking system
730. This information is stored in the user profile store 736 such
that each user is uniquely identified. The social networking system
730 also stores data describing one or more connections between
different users in the connection store 738. The connection
information may indicate users who have similar or common work
experience, group memberships, hobbies, or educational history.
Additionally, the social networking system 730 includes
user-defined connections between different users, allowing users to
specify their relationships with other users. For example,
user-defined connections allow users to generate relationships with
other users that parallel the users' real-life relationships, such
as friends, co-workers, partners, and so forth. Users may select
from predefined types of connections, or define their own
connection types as needed. Connections with other nodes in the
social networking system 730, such as non-person entities, buckets,
cluster centers, images, interests, pages, external systems,
concepts, and the like are also stored in the connection store
738.
[0131] The social networking system 730 maintains data about
objects with which a user may interact. To maintain this data, the
user profile store 736 and the connection store 738 store instances
of the corresponding type of objects maintained by the social
networking system 730. Each object type has information fields that
are suitable for storing information appropriate to the type of
object. For example, the user profile store 736 contains data
structures with fields suitable for describing a user's account and
information related to a user's account. When a new object of a
particular type is created, the social networking system 730
initializes a new data structure of the corresponding type, assigns
a unique object identifier to it, and begins to add data to the
object as needed. This might occur, for example, when a user
becomes a user of the social networking system 730, the social
networking system 730 generates a new instance of a user profile in
the user profile store 736, assigns a unique identifier to the user
account, and begins to populate the fields of the user account with
information provided by the user.
[0132] The connection store 738 includes data structures suitable
for describing a user's connections to other users, connections to
external systems 720 or connections to other entities. The
connection store 738 may also associate a connection type with a
user's connections, which may be used in conjunction with the
user's privacy setting to regulate access to information about the
user. In an embodiment of the invention, the user profile store 736
and the connection store 738 may be implemented as a federated
database.
[0133] Data stored in the connection store 738, the user profile
store 736, and the activity log 742 enables the social networking
system 730 to generate the social graph that uses nodes to identify
various objects and edges connecting nodes to identify
relationships between different objects. For example, if a first
user establishes a connection with a second user in the social
networking system 730, user accounts of the first user and the
second user from the user profile store 736 may act as nodes in the
social graph. The connection between the first user and the second
user stored by the connection store 738 is an edge between the
nodes associated with the first user and the second user.
Continuing this example, the second user may then send the first
user a message within the social networking system 730. The action
of sending the message, which may be stored, is another edge
between the two nodes in the social graph representing the first
user and the second user. Additionally, the message itself may be
identified and included in the social graph as another node
connected to the nodes representing the first user and the second
user.
[0134] In another example, a first user may tag a second user in an
image that is maintained by the social networking system 730 (or,
alternatively, in an image maintained by another system outside of
the social networking system 730). The image may itself be
represented as a node in the social networking system 730. This
tagging action may create edges between the first user and the
second user as well as create an edge between each of the users and
the image, which is also a node in the social graph. In yet another
example, if a user confirms attending an event, the user and the
event are nodes obtained from the user profile store 736, where the
attendance of the event is an edge between the nodes that may be
retrieved from the activity log 742. By generating and maintaining
the social graph, the social networking system 730 includes data
describing many different types of objects and the interactions and
connections among those objects, providing a rich source of
socially relevant information.
[0135] The web server 732 links the social networking system 730 to
one or more user devices 710 and/or one or more external systems
720 via the network 750. The web server 732 serves web pages, as
well as other web-related content, such as Java, JavaScript, Flash,
XML, and so forth. The web server 732 may include a mail server or
other messaging functionality for receiving and routing messages
between the social networking system 730 and one or more user
devices 710. The messages can be instant messages, queued messages
(e.g., email), text and SMS messages, or any other suitable
messaging format.
[0136] The API request server 734 allows one or more external
systems 720 and user devices 710 to call access information from
the social networking system 730 by calling one or more API
functions. The API request server 734 may also allow external
systems 720 to send information to the social networking system 730
by calling APIs. The external system 720, in one embodiment, sends
an API request to the social networking system 730 via the network
750, and the API request server 734 receives the API request. The
API request server 734 processes the request by calling an API
associated with the API request to generate an appropriate
response, which the API request server 734 communicates to the
external system 720 via the network 750. For example, responsive to
an API request, the API request server 734 collects data associated
with a user, such as the user's connections that have logged into
the external system 720, and communicates the collected data to the
external system 720. In another embodiment, the user device 710
communicates with the social networking system 730 via APIs in the
same manner as external systems 720.
[0137] The action logger 740 is capable of receiving communications
from the web server 732 about user actions on and/or off the social
networking system 730. The action logger 740 populates the activity
log 742 with information about user actions, enabling the social
networking system 730 to discover various actions taken by its
users within the social networking system 730 and outside of the
social networking system 730. Any action that a particular user
takes with respect to another node on the social networking system
730 may be associated with each user's account, through information
maintained in the activity log 742 or in a similar database or
other data repository. Examples of actions taken by a user within
the social networking system 730 that are identified and stored may
include, for example, adding a connection to another user, sending
a message to another user, reading a message from another user,
viewing content associated with another user, attending an event
posted by another user, posting an image, attempting to post an
image, or other actions interacting with another user or another
object. When a user takes an action within the social networking
system 730, the action is recorded in the activity log 742. In one
embodiment, the social networking system 730 maintains the activity
log 742 as a database of entries. When an action is taken within
the social networking system 730, an entry for the action is added
to the activity log 742. The activity log 742 may be referred to as
an action log.
[0138] Additionally, user actions may be associated with concepts
and actions that occur within an entity outside of the social
networking system 730, such as an external system 720 that is
separate from the social networking system 730. For example, the
action logger 740 may receive data describing a user's interaction
with an external system 720 from the web server 732. In this
example, the external system 720 reports a user's interaction
according to structured actions and objects in the social
graph.
[0139] Other examples of actions where a user interacts with an
external system 720 include a user expressing an interest in an
external system 720 or another entity, a user posting a comment to
the social networking system 730 that discusses an external system
720 or a web page 722a within the external system 720, a user
posting to the social networking system 730 a Uniform Resource
Locator (URL) or other identifier associated with an external
system 720, a user attending an event associated with an external
system 720, or any other action by a user that is related to an
external system 720. Thus, the activity log 742 may include actions
describing interactions between a user of the social networking
system 730 and an external system 720 that is separate from the
social networking system 730.
[0140] The authorization server 744 enforces one or more privacy
settings of the users of the social networking system 730. A
privacy setting of a user determines how particular information
associated with a user can be shared. The privacy setting comprises
the specification of particular information associated with a user
and the specification of the entity or entities with whom the
information can be shared. Examples of entities with which
information can be shared may include other users, applications,
external systems 720, or any entity that can potentially access the
information. The information that can be shared by a user comprises
user account information, such as profile photos, phone numbers
associated with the user, user's connections, actions taken by the
user such as adding a connection, changing user profile
information, and the like.
[0141] The privacy setting specification may be provided at
different levels of granularity. For example, the privacy setting
may identify specific information to be shared with other users;
the privacy setting identifies a work phone number or a specific
set of related information, such as, personal information including
profile photo, home phone number, and status. Alternatively, the
privacy setting may apply to all the information associated with
the user. The specification of the set of entities that can access
particular information can also be specified at various levels of
granularity. Various sets of entities with which information can be
shared may include, for example, all friends of the user, all
friends of friends, all applications, or all external systems 720.
One embodiment allows the specification of the set of entities to
comprise an enumeration of entities. For example, the user may
provide a list of external systems 720 that are allowed to access
certain information. Another embodiment allows the specification to
comprise a set of entities along with exceptions that are not
allowed to access the information. For example, a user may allow
all external systems 720 to access the user's work information, but
specify a list of external systems 720 that are not allowed to
access the work information. Certain embodiments call the list of
exceptions that are not allowed to access certain information a
"block list". External systems 720 belonging to a block list
specified by a user are blocked from accessing the information
specified in the privacy setting. Various combinations of
granularity of specification of information, and granularity of
specification of entities, with which information is shared are
possible. For example, all personal information may be shared with
friends whereas all work information may be shared with friends of
friends.
[0142] The authorization server 744 contains logic to determine if
certain information associated with a user can be accessed by a
user's friends, external systems 720, and/or other applications and
entities. The external system 720 may need authorization from the
authorization server 744 to access the user's more private and
sensitive information, such as the user's work phone number. Based
on the user's privacy settings, the authorization server 744
determines if another user, the external system 720, an
application, or another entity is allowed to access information
associated with the user, including information about actions taken
by the user.
[0143] The social networking system 730 may include a digital video
stabilization module 746. The digital video stabilization module
746 may compute a set of smooth camera orientations under the
constraint that empty regions are not visible, or below a minimum
threshold value. The digital video stabilization module 746 may
then generate warped frames based on the set of new smoothed camera
orientations. In an embodiment, the digital video stabilization
module 746 may be implemented as the digital video stabilization
400 of FIG. 4.
Hardware Implementation
[0144] The foregoing processes and features can be implemented by a
wide variety of machine and computer system architectures and in a
wide variety of network and computing environments. FIG. 8
illustrates an example of a computer system 800 that may be used to
implement one or more of the embodiments described herein in
accordance with an embodiment of the invention. The computer system
800 includes sets of instructions for causing the computer system
800 to perform the processes and features discussed herein. The
computer system 800 may be connected (e.g., networked) to other
machines. In a networked deployment, the computer system 800 may
operate in the capacity of a server machine or a client machine in
a client-server network environment, or as a peer machine in a
peer-to-peer (or distributed) network environment. In an embodiment
of the invention, the computer system 800 may be a component of the
social networking system described herein. In an embodiment of the
invention, the computer system 800 may be one server among many
that constitutes all or part of the social networking system
830.
[0145] The computer system 800 includes a processor 802, a cache
804, and one or more executable modules and drivers, stored on a
computer-readable medium, directed to the processes and features
described herein. Additionally, the computer system 800 includes a
high performance input/output (I/O) bus 806 and a standard I/O bus
808. A host bridge 810 couples processor 802 to high performance
I/O bus 806, whereas I/O bus bridge 812 couples the two buses 806
and 808 to each other. A system memory 814 and one or more network
interfaces 816 couple to high performance I/O bus 806. The computer
system 800 may further include video memory and a display device
coupled to the video memory (not shown). Mass storage 818 and I/O
ports 820 couple to the standard I/O bus 808. The computer system
800 may optionally include a keyboard and pointing device, a
display device, or other input/output devices (not shown) coupled
to the standard I/O bus 808. Collectively, these elements are
intended to represent a broad category of computer hardware
systems, including but not limited to computer systems based on the
x86-compatible processors manufactured by Intel Corporation of
Santa Clara, Calif., and the x86-compatible processors manufactured
by Advanced Micro Devices (AMD), Inc., of Sunnyvale, Calif., as
well as any other suitable processor.
[0146] An operating system manages and controls the operation of
the computer system 800, including the input and output of data to
and from software applications (not shown). The operating system
provides an interface between the software applications being
executed on the system and the hardware components of the system.
Any suitable operating system may be used, such as the LINUX
Operating System, the Apple Macintosh Operating System, available
from Apple Computer Inc. of Cupertino, Calif., UNIX operating
systems, Microsoft.RTM. Windows.RTM. operating systems, BSD
operating systems, and the like. Other implementations are
possible.
[0147] The elements of the computer system 800 are described in
greater detail below. In particular, the network interface 816
provides communication between the computer system 800 and any of a
wide range of networks, such as an Ethernet (e.g., IEEE 802.3)
network, a backplane, etc. The mass storage 818 provides permanent
storage for the data and programming instructions to perform the
above-described processes and features implemented by the
respective computing systems identified above, whereas the system
memory 814 (e.g., DRAM) provides temporary storage for the data and
programming instructions when executed by the processor 802. The
I/O ports 820 may be one or more serial and/or parallel
communication ports that provide communication between additional
peripheral devices, which may be coupled to the computer system
800.
[0148] The computer system 800 may include a variety of system
architectures, and various components of the computer system 800
may be rearranged. For example, the cache 804 may be on-chip with
processor 802. Alternatively, the cache 804 and the processor 802
may be packed together as a "processor module", with processor 802
being referred to as the "processor core". Furthermore, certain
embodiments of the invention may neither require nor include all of
the above components. For example, peripheral devices coupled to
the standard I/O bus 808 may couple to the high performance I/O bus
806. In addition, in some embodiments, only a single bus may exist,
with the components of the computer system 800 being coupled to the
single bus. Furthermore, the computer system 800 may include
additional components, such as additional processors, storage
devices, or memories.
[0149] In general, the processes and features described herein may
be implemented as part of an operating system or a specific
application, component, program, object, module, or series of
instructions referred to as "programs". For example, one or more
programs may be used to execute specific processes described
herein. The programs typically comprise one or more instructions in
various memory and storage devices in the computer system 800 that,
when read and executed by one or more processors, cause the
computer system 800 to perform operations to execute the processes
and features described herein. The processes and features described
herein may be implemented in software, firmware, hardware (e.g., an
application specific integrated circuit), or any combination
thereof.
[0150] In one implementation, the processes and features described
herein are implemented as a series of executable modules run by the
computer system 800, individually or collectively in a distributed
computing environment. The foregoing modules may be realized by
hardware, executable modules stored on a computer-readable medium
(or machine-readable medium), or a combination of both. For
example, the modules may comprise a plurality or series of
instructions to be executed by a processor in a hardware system,
such as the processor 802. Initially, the series of instructions
may be stored on a storage device, such as the mass storage 818.
However, the series of instructions can be stored on any suitable
computer readable storage medium. Furthermore, the series of
instructions need not be stored locally, and could be received from
a remote storage device, such as a server on a network, via the
network interface 816. The instructions are copied from the storage
device, such as the mass storage 818, into the system memory 814
and then accessed and executed by the processor 802. In various
implementations, a module or modules can be executed by a processor
or multiple processors in one or multiple locations, such as
multiple servers in a parallel processing environment.
[0151] Examples of computer-readable media include, but are not
limited to, recordable type media such as volatile and non-volatile
memory devices; solid state memories; floppy and other removable
disks; hard disk drives; magnetic media; optical disks (e.g.,
Compact Disk Read-Only Memory (CD ROMS), Digital Versatile Disks
(DVDs)); other similar non-transitory (or transitory), tangible (or
non-tangible) storage medium; or any type of medium suitable for
storing, encoding, or carrying a series of instructions for
execution by the computer system 800 to perform any one or more of
the processes and features described herein.
[0152] For purposes of explanation, numerous specific details are
set forth in order to provide a thorough understanding of the
description. It will be apparent, however, to one skilled in the
art that embodiments of the disclosure can be practiced without
these specific details. In some instances, modules, structures,
processes, features, and devices are shown in block diagram form in
order to avoid obscuring the description. In other instances,
functional block diagrams and flow diagrams are shown to represent
data and logic flows. The components of block diagrams and flow
diagrams (e.g., modules, blocks, structures, devices, features,
etc.) may be variously combined, separated, removed, reordered, and
replaced in a manner other than as expressly described and depicted
herein.
[0153] Reference in this specification to "one embodiment", "an
embodiment", "other embodiments", "one series of embodiments",
"some embodiments", "various embodiments", or the like means that a
particular feature, design, structure, or characteristic described
in connection with the embodiment is included in at least one
embodiment of the disclosure. The appearances of, for example, the
phrase "in one embodiment" or "in an embodiment" in various places
in the specification are not necessarily all referring to the same
embodiment, nor are separate or alternative embodiments mutually
exclusive of other embodiments. Moreover, whether or not there is
express reference to an "embodiment" or the like, various features
are described, which may be variously combined and included in some
embodiments, but also variously omitted in other embodiments.
Similarly, various features are described that may be preferences
or requirements for some embodiments, but not other
embodiments.
[0154] The language used herein has been principally selected for
readability and instructional purposes, and it may not have been
selected to delineate or circumscribe the inventive subject matter.
It is therefore intended that the scope of the invention be limited
not by this detailed description, but rather by any claims that
issue on an application based hereon. Accordingly, the disclosure
of the embodiments of the invention is intended to be illustrative,
but not limiting, of the scope of the invention, which is set forth
in the following claims.
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